obs-duplicates: Find duplicate packages across OBS projects

Sometimes we end up having the same package in two different projects, usually both in :development and in the :sdk, which is undesiderable and can easily mislead people.

See also apertis-jenkins-jobs!79 (merged).

Test run: https://jenkins.apertis.org/view/apertis-v2021dev1/job/apertis-v2021dev1/job/health/job/obs-duplicates-target+development+sdk/12/